1. Field of the Invention
The present invention relates to a chemical-mechanical wafer polishing device, and more particularly to a device for polishing the surface of a wafer by causing friction between a polishing pad and a wafer while supplying slurry (including a polishing agent) to the surface of the polishing pad.
2. Description of the Prior Art
Wafers, which are used to manufacture integrated circuits and other types of electronic elements, are fabricated through a process of depositing multiple layers, which are made of a conductive material, a semi-conductive material, and a dielectric material, on the surface of a substrate or removing the same.
The surface of a wafer, fabricated in this manner, becomes non-planar while going through the deposition or removal process, and is therefore planarized through a polishing process.
As a kind of device for polishing wafers, a chemical-mechanical wafer polishing device is used, which polishes the surface of a wafer by causing friction between the wafer and a polishing pad while supplying slurry (including a polishing agent) to the surface of the polishing pad.
The process of polishing a wafer using the polishing pad is conducted while the wafer is pressurized to contact the polishing pad (normally 5-7 psi) and then rotated; as a result, frictional heat is generated during the polishing process, and the frictional heat increases the surface temperature of the wafer, thereby causing a temperature deviation on the surface of the wafer.
The rate of polishing of the surface of a wafer has a correlation with the surface temperature of the wafer (the higher the surface temperature is, the faster the polishing proceeds); therefore, in order to stably maintain the flatness of the wafer, a chemical-mechanical wafer polishing device has been devised and used, which has a cooling fluid supply portion for cooling the heat generated by friction between the wafer and the polishing pad.
FIG. 15 is a perspective view illustrating assembled major parts of a conventional chemical-mechanical polishing device, and FIG. 16 is a sectional view illustrating major parts of the conventional chemical-mechanical polishing device.
The conventional chemical-mechanical wafer polishing device, as illustrated in the drawings, includes: a polishing pad 111; a polishing head 120 installed on the upper side of the polishing pad 110 so as to lie opposite the polishing pad 111; a membrane 140, which is installed on the polishing head 120 so as to face the polishing pad 111; a chamber pressure adjustment portion 113, which is installed on the upper side of the polishing head 120, and which has a nitrogen fluid supply line 113a; and a cooling gas supply portion 150 configured to eject nitrogen gas towards the polishing pad 111.
The polishing pad 111 is driven by a predetermined driving unit. The configuration of the driving unit is widely known in the art, and a detailed description thereof will be omitted herein.
The polishing head 120 includes a retaining ring 121, which has the shape of a circular tube, and an upper ring 122 and a plate 123, which is arranged in the vertical direction inside the retaining ring 121.
Each of the upper ring 122 and the plate 123 has a gas inflow hole formed thereon, respectively.
The polishing head 120 is driven to rotate by a predetermined driving unit, in conformity with the wafer polishing process, or is driven to move linearly towards and away from the polishing pad 111. The configuration of the driving unit is widely known in the art, and a detailed description thereof will be omitted herein. Reference numeral 112a denotes a rotating shaft that constitutes the driving unit.
The membrane 140 is formed in a concave shape. The concave space of the membrane 140 forms a chamber 144.
The nitrogen gas supply line 113a is installed to be connected to the gas inflow hole of the upper ring 122.
The chamber pressure adjustment portion 113, as widely known in the art, adjusts the pressure inside the chamber 144 such that, by generating a positive pressure state or a negative pressure state inside the chamber 144, a drawing force, which draws the bottom surface of the membrane 140 towards the polishing head 120, and a pressurizing force, which pressurizes the bottom surface of the membrane 140 towards the polishing pad 111, can be selectively applied on the chamber 144. The pressure adjustment by the chamber pressure adjustment portion 113 is controlled in conformity with the wafer polishing process. The configuration of the chamber pressure adjustment portion 113 is widely known in the art, and a detailed description thereof will be omitted herein.
The cooling gas supply portion 150 includes an ejection tube 151, which is installed approximately at the same height as the wafer 201, and a connecting tube 152, which connects between the ejection tube 151 and the nitrogen gas supply line 113a. 
The ejection tube 151 is installed to surround the retaining ring 121.
The ejection tube 151 has multiple ejection holes 151a formed thereon.
Subordinate features for supplying and recovering the cooling gas (electronic opening/closing valve) are widely known in the art, and a detailed description thereof will be omitted herein.
The time of supply of the cooling gas by the cooling gas supply portion 150 is controlled in conformity with the other wafer polishing processes.
The operation of the cooling gas supply portion 150 of the conventional chemical-mechanical wafer polishing device, which has the above-mentioned configuration, will now be described. It will be assumed, for convenience of description, that the polishing head 120 is positioned on the upper side of the polishing pad 111, and the wafer 201 contacts the upper surface of the polishing pad 111 while adhering to the bottom surface of the membrane 140 by means of the drawing force applied to the bottom surface of the membrane 140.
The control unit initially controls the chamber pressure adjustment portion 113 such that nitrogen gas is supplied to the chamber 144 through the nitrogen gas supply line 113a. After the nitrogen gas is supplied through the nitrogen gas supply line 113a, a pressurizing force is applied to the bottom surface of the membrane 140 such that the same is pressurized towards the polishing pad 111, and the wafer 201 is accordingly pressurized to contact the polishing pad 111.
The nitrogen gas, which is supplied through the nitrogen gas supply line 113a, successively moves through the connecting tube 152 and the ejection tube 151, and is finally ejected towards the polishing pad 111 through the ejection hole 151a. 
The polishing head 120 and the polishing pad 111 are then rotated in opposite directions, thereby polishing the wafer 201.
The wafer 201, which is being polished, is cooled by the nitrogen gas ejected towards the polishing pad 111.
The conventional chemical-mechanical wafer polishing device has a problem in that, since the wafer 201, which is subjected to the polishing process, is cooled by the nitrogen gas ejected towards the polishing pad 111 through the ejection tube 151, which is installed to surround the retaining ring 121, the peripheral area of the wafer is mainly cooled, while the central area thereof is not properly cooled.
Such partial cooling of only the peripheral area of the wafer, with poor cooling of the central area of the wafer, results in a secondary problem in that the polishing of the central area of the wafer is accelerated, making it impossible to stably maintain the flatness of the wafer.
An example of a relevant prior art document is Korean Patent Publication No. 10-2003-0050105 (entitled “CHEMICAL MECHANICAL POLISHING APPARATUS”, published on Jun. 25, 2003), and this prior art document discloses a technology regarding the conventional chemical-mechanical polishing device described above.